Glyn M Ruck

Some of the best technical minds on the board reside on the w203 forum.

Would you guys please take a look at this W204 thread.

https://mbworld.org/forums/c-class-w...ys-normal.html

Boom vang

If you are not losing any fluid then the problem lies with an internal leaking master cylinder, air trapped in the m/c or a bad ABS distribution unit that is bleeding off the pressure to the fronts

I had a problem with trying to get all the air out of the Master cylinder, conventional bleeding would not do it and it had to be bench bleed to get it working properly as I had similar symptoms (this was for a different make of car BTW) The brakes would work but eventually sink to the floor yet no air came out of the calipers. Once I bench bled it, I had an nice firm pedal.

http://autorepair.about.com/od/fixit...ench-bleed.htm

Silver C

Bleeding the brakes would probably be the best way to go, have a friend step on the brakes while you bleed it so it clears out all trapped air. You might want to do it more than once to make sure you got all the air out..

Glyn M Ruck

These brakes have been pressure bled to WIS method multiple times.

johnand

I would tend to agree with the guy that is pointing the finger at the ABS unit. Pressure bleeding correctly removes all the trapped air in a brake hydraulic system.

lkfoster

By a process of elimination I would suspect the ABS also. The calipers are out because you'd see the leak and hose flexing is visible also leaving the MC which is new.

The "yeah, but..." here is that new parts have been known to be defective from time to time. Having said that I don't know of any way to diagnose the MC in isolation other than pulling all of the lines off and plugging the ports. That, or throwing another one in. Neither option is particularly attractive, but at least they're easier than getting MBSA to cover a replacement ABS module.

e1000

Wow, that's dangerous. There's no feeling as bad as going for your brakes and not having them grab. It's terrifying.

Glyn M Ruck

See ABS schematics here in post 24

https://mbworld.org/forums/c-class-w...ys-normal.html

Silver C

Glyn, this may sound cheesy, but ruling everything out, have they checked the brake pedals itself? Maybe, just maybe, there is somewith wrong with the pedal or aroundabout. Its awkward that there is no fluid loss despite loss of pressure, which doesn't make sense to me. Especially if we have already ruled out air bubbles as well.. Regarding the abs, if there is a fault or a leak there, shouldn't the malfunction notification pop up?

Silver C

Or, just came up to my mind, since mbsa is not replacing the SBA unit, is it possible to find someone around the area that can do an abs unit swap? See if problem persists. Or encourage mbsa to do the swap for you.

lkfoster

Looking at the diagrams I now doubt that it's the ABS, there's no place for the fluid to go unless it's leaking externally or if there's an air bubble somewhere inside.

All of the internal circuits maintain the same volume of fluid with the possible exception of the accumulators but I would not expect them to be large enough to account for the fluid being displaced by the MC.

Trapped air within the ABS could account for the pedal going down, but I have to assume that the MBSA techs have already cycled the ABS a number of times which should purge any air.

Going back to the basics, either there's a leak somewhere or the MC seals are bleeding past. Throughout all of this has the MC fluid level changed any?

What happens to the pedal if you cycle it again after it's reached the floor?

Are there any other components in the system besides the ABS? My older BMWs and Audis had pressure regulators on the rear circuits that adjusted brake line pressure based on rear ride height. I'd check my factory workshop manual but apparently it doesn't like my new 64-bit PC.

Silver C

Any progress Glyn?

Glyn M Ruck

Still in stalemate with MBSA - Consumer organisations, press etc contacted. Will take a while to get moving.

mskembo

I was just looking through all the technical service buletins, and came across this:

9 of 22: SERVICE BRAKES, AIR:ANTILOCK
Bulletin Date: JAN 2009MERCEDES VEHICLE: THE ANTI-LOCK BRAKE SYSTEM (ABS) RETURN FLOW PUMP RUNNING WITHOUT CONTROL WITH CORRESPONDING FAULT CODE C1401, CLEAN AND INSULATED THE CONNECTOR FOR THE RETURN FLOW PUMP RELAY. MODELS 202 AND 208. MODEL YEARS UNKNOWN.
I know it says 202 and 208, but I wonder if it needs to be expanded. seems like a very similar issue.

mskembo

OK, there is another brake related one...

10 of 22: SERVICE BRAKES, AIR:ANTILOCK:CONTROL UNIT/MODULE
Bulletin Date: JAN 2009MERCEDES VEHICLE: THE ANTI-LOCK BRAKE SYSTEM (ABS) RETURN FLOW PUMP RUNNING WITHOUT CONTROL WITH CORRESPONDING FAULT CODE C1401, CLEAN AND INSULATED THE CONNECTOR FOR THE RETURN FLOW PUMP RELAY. MODELS 202 AND 208. MODEL YEARS UNKNOWN.
Probably doesn't help, but it can't hurt...

Glyn M Ruck

Thanks - we will check. See main thread for progress.

Glyn M Ruck

The brown is hitting the fan - the press assault begins & top Google search status.

Benz collected car on a flatbed this morning.

Will keep the forum apprised.

mskembo

so the battle has been won, but a war is yet to be fought?

Glyn M Ruck

Well - after MBSA was prepared to commit crap to writing in this regard.

A different dealership with a decent, competent Afrikaans Service Manager with a "can do" attitude has replaced the Hydraulic Control Unit - bled & calibrated the brakes/ESP/BAS etc. & all is now repaired.

The car went through roadworthy evaluation successfully yesterday afternoon.

Keith Radue is now a far happier man after all the time his vehicle has been off the road. He will keep his blog updated with all the latest documentation.

What remains to be answered is what at a regular front pad exchange damaged the HCU - too much pressure applied pushing back calliper pistons? Dirt pushed back into the HCU & circulated by the pump? Who knows?

https://mbworld.org/forums/c-class-w...ys-normal.html

johnand

Glyn,

Glad to see it resolved So, the conclusion is the pad change damaged the HCU? If that is the case, I see that as a good reason to keep opening the caliper bleeder when compressing the pistons, as I have been doing for years. I know John (Splinter) does the same and has recommended it several times to others when changing pads.

Glyn M Ruck

John - I'm not sure what the conclusion is (see main thread) - but I would believe that if your car is fitted with an ATe ABS block, cracking open the bleed screw to relieve pressure would be wise.

anonymousmoose

Ja, it makes a massive difference finding someone who will help. I tell you, I'd be a little uneasy owning my Benz if I didn't have my warranty and a good dealer (which my Father knows the owner of) to back it up.

I went to my local MB dealer last week to ask about an AUX Audio Connector installation. The chaps there just looked in their computer and quoted me over $600 get my ipod hooked up and told me the AUX connector wasn't possible. But I KNEW this was not true because of this forum. Went to a specialist and yes, its possible. Hopefully getting the OEM AUX lead added this week or next (when the part comes in).

I'm not saying MB lied to me, its just that they go on what their computer tells them and not know-how. Plus they don't really want to investigate much even though I explained to them where to look. After I get my AUX installed, I may write their service department a friendly (not being sarcastic, it will be friendly) email to tell them there is a MB AUX lead plug-play compatible which they said there isn't. But I'll wait until its installed in case I and the specialist is wrong.

As soon as something breaks, I'll know if I made the right choice in paying for that warranty.